Amyloidosis is a progressive, incurable metabolic disease of unknown cause characterized by abnormal deposits of protein in one or more organs or body systems. Amyloid proteins are manufactured, for example, by malfunctioning bone marrow. Amyloidosis, which occurs when accumulated amyloid deposits impair normal body function, can cause organ failure or death. It is a rare disease, occurring in about eight of every 1,000,000 people. It affects males and females equally and usually develops after the age of 40. At least 15 types of amyloidosis have been identified. Each one is associated with deposits of a different kind of protein.
The major forms of amyloidosis are primary systemic, secondary, and familial or hereditary amyloidosis. There is also another form of amyloidosis associated with Alzheimer's disease. Primary systemic amyloidosis usually develops between the ages of 50 and 60. With about 2,000 new cases diagnosed annually, primary systemic amyloidosis is the most common form of this disease in the United States. Also known as light-chain-related amyloidosis, it may also occur in association with multiple myeloma (bone marrow cancer). Secondary amyloidosis is a result of chronic infection or inflammatory disease. It is often associated with Familial Mediterranean fever (a bacterial infection characterized by chills, weakness, headache, and recurring fever), Granulomatous ileitis (inflammation of the small intestine), Hodgkin's disease, Leprosy, Osteomyelitis and Rheumatoid arthritis.
Familial or hereditary amyloidosis is the only inherited form of the disease. It occurs in members of most ethnic groups, and each family has a distinctive pattern of symptoms and organ involvement. Hereditary amyloidosis is though to be autosomal dominant, which means that only one copy of the defective gene is necessary to cause the disease. A child of a parent with familial amyloidosis has a 50-50 risk of developing the disease.
Amyloidosis can involve any organ or system in the body. The heart, kidneys, gastrointestinal system, and nervous system are affected most often. Other common sites of amyloid accumulation include the brain, joints, liver, spleen, pancreas, respiratory system, and skin.
Alzheimer's disease (AD) is the most common form of dementia, a neurologic disease characterized by loss of mental ability severe enough to interfere with normal activities of daily living, lasting at least six months, and not present from birth. AD usually occurs in old age, and is marked by a decline in cognitive functions such as remembering, reasoning, and planning.
Between two and four million Americans have AD; that number is expected to grow to as many as 14 million by the middle of the 21st century as the population as a whole ages. While a small number of people in their 40 s and 50 s develop the disease, AD predominantly affects the elderly. AD affects about 3% of all people between ages 65 and 74, about 20% of those between 75 and 84, and about 50% of those over 85. Slightly more women than men are affected with AD, even when considering women tend to live longer, and so there is a higher proportion of women in the most affected age groups.
The accumulation of amyloid Aβ-peptide in the brain is a pathological hallmark of all forms of AD. It is generally accepted that deposition of cerebral amyloid Aβ-peptide is the primary influence driving AD pathogenesis. (Hardy J and Selkoe D. J., Science. 297: 353-356, 2002).
Imaging techniques, such as positron emission tomography (PET) and single photon emission computed tomography (SPECT), are effective in monitoring the accumulation of amyloid deposits in the brain and correlating it to the progression of AD (Shoghi-Jadid et al. The American journal of geriatric psychiatry 2002, 10, 24; Miller, Science, 2006, 313, 1376; Coimbra et al. Curr. Top. Med. Chem. 2006, 6, 629; Nordberg, Lancet Neurol. 2004, 3, 519). The application of these techniques requires the development of radioligands that readily enter the brain and selectively bind to amyloid deposits in vivo.
A need exists for amyloid binding compounds that are non-toxic and can cross the blood-brain barrier, and consequently, can be used in diagnostics. Furthermore, it is important to be able to monitor the efficacy of the treatment given to AD patients, by measuring the effect of said treatment by measuring changes of AD plaque level.
Properties of particular interest of a detectable amyloid binding compound, besides high affinity for amyloid deposits in vivo and high and rapid brain entrance, include low unspecific binding to normal tissue and rapid clearance from the same. These properties are commonly dependant on the lipophilicity of the compound (Coimbra et al. Curr. Top. Med. Chem. 2006, 6, 629). Based partly on the relatively higher clearance from normal brain tissue as compared to related analogues, [11C]PIB was selected from amongst these for further evaluations in human subjects (Mathis et al. J. Med. Chem. 2003, 46, 2740). Subsequently, a study on the use of [11C]PIB for the detection of amyloid deposits in-vivo in the human by the PET-technique was conducted (Klunk et al. Ann Neurol. 2004, 55, 306). In this study, significant higher retention of [11C]PIB in relevant regions of the brain, was observed in subjects with diagnosed AD as compared to healthy controls. Related methods and derivatives are described in WO 2002/16333 and WO 2004/083195.
There is a need for improved compounds in order to obtain a signal-to-noise ratio high enough to allow detailed detection of amyloid deposits throughout all brain regions, and providing improved reliability in quantiative studies on amyloid plaque load in relation to drug treatments.
The present invention provides heteroaryl substituted benzothiazole derivatives that carry such unexpected improvements over known benzothiazole derivatives providing inter alia advantageously associated low unspecific binding and rapid brain clearance.